Automatic freezing point measuring apparatus



PP y April 21, 1953 E. c. STAEHLING $635,455

' AU{OMATIC FREEZING POINT MEASURING APPARATUS Filed July 2, 1951 Hea/ing or Coo/17 9 Cyc/e Mea /um 50/6/70/0 l/a/l/e 52 Air Tempera/ure Recorder A TTORNEYS Patented Apr. 21, 1953 AUTOMATIC FREEZING POINT MEASURING APPARATUS Edward C. Staehling, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Application July 2, 1951, Serial No. 234,770

2 Claims.

This invention relates to apparatus for determining and recording automatically the freezing point of liquids. It relates in particular to such an apparatu which makes its determinations while immersed in the liquid being tested.

Many commercially significant materials are required to meet rigid purity specifications before they can be sold. In the case of organic chemical compounds, various means are used to verify the quality of the materials. Among the characteristics which may be used as an index of the purity of a compound is its freezing point. In continuous production operations, it would be convenient and desirable to be able to have a record of the freezing point of the product at frequent intervals. In those chemical reactions in which an end point may be recognized by the freezing point of the desired product, it would be most helpful to have a record of the changes in freezing point of the reaction mixture so that, as the desired end point is approached, suitable steps may be taken toward termination of the reaction. In cases of the types mentioned, a useful apparatus would be a freezing point recording apparatus which is capable of making its determinations automatically, at frequent intervals, and at a point beneath the surface of the body of liquid being tested so that the samples tested are truly representative of the whole. The provision of such an apparatus is the principal object of the present invention.

The apparatus of the present invention comprises a sampling chamber immersed in the liquid to be tested, jacketed for circulation thereabout of a heat transfer medium, preferably insulated against thermal effects of the surrounding liquid, and having an inlet and an outlet for the liquid to be tested, means for opening and for closing both said inlet and said outlet, an agitator in said chamber, means for driving said agitator, continuous temperature recording means to indicate the temperature within the chamber, and means for controlling the intervals at which the sample in the chamber is changed.

The single figure of the accompanying draw:

ing is an elevation and partial vertical section of the new apparatus, with a schematic representation of control means therefor.

Referring to the drawing, freezing chamber In is immersed beneath the liquid N to be tested in a tank or reaction vessel |2, being suspended from the coverplate l3 of tank |2 by means of hangers I4. Chamber I is fitted with a coaxial stirrer or agitator |5, driven by an externally mounted motor l6, and is provided with an inlet l1 and an outlet I8 for samples of the liquid N to be tested. Chamber I0 is surrounded, at least on its vertical walls, by jacket l9, providing a space 20 for circulation of heating or cooling fluid which may enter space 2|] through pipe 2| and may leave through pipe 22. Chamber H3, its surrounding jacketed space 20', and the coolant inlet pipe 2| may be protected against thermal effects of the surrounding liquid N by means of an additional jacket 23, providing an insulating air space 24. Sample inlet IT and outlet I8 are provided with removable cover plates or other full opening valve means or closures 25, mounted to operate simultaneously on rod 26, which is illustrated as being actuated by an airlift motor 21. At a point preferably near the center of chamber In is mounted a thermoelement Z8 having leads 29 to a temperature recorder 3|]. The remaining parts of the apparatus comprise a cycle controller, or timer 3|, for starting and stopping the flow of cooling fluid through pipe 2| and for closing and opening the ports I! and |8 of the sample chamber Hi. In the illustrated embodiment, controller 3| admits current at intervals to a solenoid 32, which actuates a valve 33, and the latter, when open, admits an air stream to an air operated valve 34 in line 2| and to the airlift motor 21.

In operation, motor I6 is operated continuous- 1y, turning the shaft of agitator IS, the pitched blades of which draw liquid N through inlet into chamber |D and expel it through outlet I8. When cycle controller 3| closes the electrical circuit through solenoid 32, valv 33 is opened, and an air stream causes motor 2'! to operate, lifting cover plates 25 on shaft 26 into position to close ports I! and I8. At the same time, the valve 34 is opened, and cooling fluid is circulated from pipe 2| through jacketed space 20 and out through pipe 22. Agitator 15 keep the confined sample in chamber it in motion, and uniform cooling occurs by heat transfer from the sample, through the wall of chamber NJ, to the coolant in space 2|]. A continuous temperature record is made by the recorder 30. When valves 25 are closed and cooling starts, there is a rapid drop in temperature until thefreezing point is reached, when the temperature of the agitated and confined sample becomes fixed, as the freezing liquid is in equilibrium with its crystals. Thereafter, the cycle controller 3| opens the circuit to solenoid 32, closing valves 33 and 34 and stopping motor 21. Shaft 26 and valve members 25 drop, opening ports I! and I8. The partially solidified sample in chamber H) is melted by entry of hot liquid ,that of the single desired end product.

3 l I through port I1, and is displaced through outlet I8. The timer element of controller 3| is set to allow chamber to reach the temperature of liquid l I, and to be flushed free of all the previous charge, before the above-described cycle is repeated. The time consumed in a Single cycle between two freezing point determinations may be as long as desired, or it may be as brief as the time required to reduce the temperature of the liquid sample to its freezing point and to displace that sample from the chamber with a new sample. The greater the differential between the liquid temperature and its freezing point, the longer Will be the time required to determine the freezing point, using cooling fluid at a fixed tempera ture below the freezing point of the liquid. Similarly, the greater the differential between the freezing point of the liquid and the lower temperature of the cooling fluid, the shorter will be the time required to cool the sample to its freezing point, other factors being constant.

An apparatus of the type described has been installed in a reaction vessel in which a compound of low freezing point is converted to one with a freezing point near 200 C. During the ,course of the reaction a large number of intermediate products, each having several isomeric forms, is produced, and the freezing point of the mixtures range from sub-zero temperatures to important that the reaction be stopped at the desired point, since further reaction produces a compound which not only has a very much lower freezing point but also has an entirely different chemical structure and cannot be used for the purposes for which the desired product is used. Before the installation of the present apparatus it was most difficult to detect the proper point for terminating the reaction, and batches might be carried too far, or stopped short of the desired point. Owing to the viscous character of the mix, representative samples were difficult to obtain and, by the time they could be checked for freezing point, the reaction could easily have progressed too far. Since installation of the new apparatus, clean and representative samples are taken within the body of the reaction mixture and their freezing points are measured at intervals of 2 to 6 minutes, the intervals diminishing as the end point is approached. The reaction is traced by the recorded freezing points, and is discontinued within minutes of the recording of the proper value for the desired product.

The invention, then, oifers the advantages of operating automatically, taking representative It is 4 samples of the batch being tested, making frequent determinations of the freezing point of the batch, and returning the samples to the batch without waste or danger of contamination.

I claim:

1. Apparatus for determining automatically the freezing point of a liquid, comprising a jacketed sampling chamber to be immersed in the liquid to be tested, said chamber being jacketed for circulation thereabout of a coolant which is fluid at temperatures below the freezing point of the liquid being tested, an inlet and an outlet in the sampling chamber for the test liquid, means for opening and for closing both said inlet and said outlet, an agitator in said chamber serving both to stir the test liquid and to cause the same to flow through said outlet and inlet on opening thereof, means for driving said agitator, continuous temperature recording means connected with said chamber for indicating the temperature therein, and means for controlling the intervals at which the inlet and outlet of the chamber are opened and closed.

2. Apparatus for determining automatically the freezing point of a liquid, comprising a jacketed sampling chamber to be immersed in the liquid to be tested, said chamber being jacketed for circulation thereabout of a coolant which is fluid at temperatures below the freezing point of the liquid being tested, an inlet and an outlet in the sampling chamber for the test liquid, coacting means for opening and for closing both said inlet and said outlet simultaneously, a propeller type agitator in said chamber serving both to stir the test liquid and to cause the same to flow through said outlet and inlet on opening thereof, means for driving said agitator continuously, continuous temperature recording means connected with said chamber for indicating the temperature therein, means for controlling the intervals at which the inlet and outlet of the chamber are opened and closed, and means actuated by the last said means for circulating a cooling fluid through the jacket of the chamber while the inlet and outlet to the chamber are closed.

EDWARD C. STAEHLING.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,189,785 Brown July 4, 1916 2,297,641 Webber Sept. 29, 1942 2,591,084 Martin Apr. 1, 1952 

